Hacking The Kendama With Physics

Michael hands Hannah a kendama, the Japanese cup-and-ball toy, and asks her to land a single catch. Then he brings out one built for him by Adam Savage of MythBusters and explains why a heavier kendama is a completely different physics problem. A kendama looks like a children's toy. It is really a pendulum, a lesson in angular momentum and a catching problem borrowed from spacecraft docking. Michael and Hannah get into why the swing timing barely changes when the ball gets heavier, why the trick is to match the ball's velocity rather than grab at it, why bending your knees on the catch is doing real work, and why the paint finish on a kendama changes how it plays. Then Hannah and Michael take on your questions: what would actually happen if you flew into Jupiter and kept going, whether there is a mathematical way to swim faster, and which books they'd hand an adult who wants to get back into maths after school ruined it. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit https://cancerresearchuk.org/restisscience Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ." ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Adam Thornton + Oli Oakley + Jack Meek Animator: Sam Benson Video & Social: Bex Tyrrell Assistant Producer: Lucy Lipscombe Producer: Simona Rata Senior Producer: Lauren Armstrong-Carter Chief Digital Officer: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

• 0:01Speaker 00

  Hello and welcome to The Rest Is Science. I'm Michael Stevens.

• 0:03Speaker 01

  And I'm Hannah Fry.

• 0:04Speaker 00

  And today on Field Notes, I have brought you a gift, Hannah.

• 0:08Speaker 01

  My favorite kind of field notes.

• 0:10Speaker 00

  There you go. Your very own Kendama.

• 0:14Speaker 01

  Okay. Is it like a cup and ball?

• 0:16Speaker 00

  It's a cup and ball. It's a, a style of the cup and ball game. You've basically got this wooden stick with two cups on either side and one on the bottom and a string attaches. I got scissors for you.

• 0:28Speaker 01

  Thank you.

• 0:29Speaker 00

  It's, you've also got a, a string that attaches a wooden ball to the stick. And you just get to swoop the ball up and catch it in the cups on the stick. Or because there's a hole in the ball, you can catch it on a spike.

• 0:44Speaker 01

  Ooh.

• 0:44Speaker 00

  Right now, in the package, it's sitting on that spike.

• 0:48Speaker 01

  So hold on a second. This is, it's, it's like a more complicated version of cup and ball.

• 0:53Speaker 00

  Exactly.

• 0:54Speaker 01

  Where you have more options.

• 0:56Speaker 00

  You've got more options. You can do a lot more tricks and you can also do a lot of physics with it.

• 1:00Speaker 01

  Are you really good at this?

• 1:02Speaker 00

  I don't think so.

• 1:03Speaker 01

  Okay.

• 1:04Speaker 00

  Those of you in this room that saw me practicing while Hannah was out of the room, you know how bad I am. I did try to get really good. When I was on tour with Adam Savage, a fan gave me one and I just played with it all day on tour and I got, I thought I got pretty good.

• 1:21Speaker 01

  This is saying it's a classic Japanese skill toy.

• 1:24Speaker 00

  Exactly. And that's why it's called a Kendama. So the Ken is what you call the stick, the spike cupped stick and the Dama is the Japanese word for the ball.

• 1:34Speaker 01

  Right.

• 1:35Speaker 00

  So it is a Kendama. Those are its two parts.

• 1:37Speaker 01

  I mean, thus far, it's been quite a struggle to even get it out of its packaging. So I'm not sure this is going to go that well.

• 1:49Speaker 00

  This episode is brought to you by Cancer Research UK.

• 1:51Speaker 01

  As if they weren't cool enough already, some astronauts have now added cancer scientists to their CUP. They are making use of microgravity conditions in space to carry out experiments.

• 2:02Speaker 00

  That's because the same thing that lets astronauts experience weightlessness also affects how cancer cells grow, behave and respond to drugs.

• 2:11Speaker 01

  And back down on Earth, Cancer Research UK is working with astronomers to explore tumors with technologies that are typically used to map the Milky Way, which I think gives you an idea of just how complex this disease is.

• 2:24Speaker 00

  That's right. There are over 200 different types of cancer, but by pushing boundaries and embracing the latest technologies, Cancer Research UK has helped double cancer survival in the UK over the past 50 years.

• 2:36Speaker 01

  And today it is continuing to save and improve lives around the world. For more information about Cancer Research UK, their research and breakthroughs, and how you can support them, visit cancerresearchuk.org/restiscience.

• 2:49Speaker 02

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• 3:20Speaker 03

  This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome, that's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration blog, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense? There's no place like Chrome. Check responses set up required. Compatibility and availability varies. 18 plus.

• 3:52Speaker 00

  I want you to try to spike the ball.

• 3:56Speaker 01

  Okay.

• 3:56Speaker 00

  Flip it up and I'll, I'll give you one tip.

• 3:59Speaker 01

  Uh huh.

• 4:00Speaker 00

  It helps to start by just letting the ball hang all the way down to the ground and then unwrap it a little bit more. There we go. And then pull it straight up because the hole is on the bottom of the ball. So if you pull it straight up and you get it to fall onto the spike, it might. Okay. Yeah. So you've got the technique down, but that hole was not in the right place.

• 4:25Speaker 01

  I mean, no, definitely not. Imagine if I, imagine if I'm amazing at this.

• 4:30Speaker 00

  That would ruin the entire episode because of what I'm going to show you next.

• 4:35Speaker 01

  Every time I try something new, there is a little bit of my brain, which is like, this might be the thing.

• 4:39Speaker 00

  This might be what I was born to do.

• 4:41Speaker 01

  It's never the thing.

• 4:42Speaker 00

  It's never been true.

• 4:44Speaker 01

  It's been true, but still every time, every time. Okay. Actually, that's not true. Once I went clay pigeon shooting and I really was.

• 4:49Speaker 00

  And you really were a natural.

• 4:50Speaker 01

  Amazing at it.

• 4:51Speaker 00

  And you continued to be amazing as you.

• 4:53Speaker 01

  Oh yeah. I mean, I've only done it once, but I was amazing.

• 4:57Speaker 00

  All right. Let's try this one more time at least. Okay. So you're, you're hitting the ball with the spike, but you want to, you want to get into the little hole.

• 5:03Speaker 01

  All right. What is this? We're back to, oh, I'm not getting it quite. It's not quite the right angle. Hang on. How many, is the entire episode just watching me do this until I?

• 5:14Speaker 00

  Yeah, we cannot stop recording until you succeed.

• 5:18Speaker 01

  What I want you to do is, um, uh, I'd like to, uh, do this as many times as it takes to get it in. And then I want you to cut the episode so that it looks like I got it in first time. Okay. You're right.

• 5:31Speaker 00

  It might help if you were standing, to be honest, because it's hard to get the angle just right. Oh, that was close.

• 5:41Speaker 00

  You've made contact every time.

• 5:43Speaker 01

  This is, this is fun to learn and difficult to master.

• 5:46Speaker 00

  Yeah.

• 5:47Speaker 01

  Okay, okay, okay. I'm just going to do three more and then, then I'm going to give up.

• 5:50Speaker 00

  Okay.

• 5:51Speaker 01

  Damn it. Can you do it?

• 5:53Speaker 00

  Maybe.

• 5:57Speaker 01

  Go on, go on, go on, go on. God, you're so close.

• 6:03Speaker 01

  Okay.

• 6:04Speaker 00

  So.

• 6:04Speaker 01

  Was that fun to master?

• 6:06Speaker 00

  Uh, I haven't mastered it yet, but I'm having fun trying. It was definitely easy to learn.

• 6:11Speaker 01

  Yeah.

• 6:12Speaker 00

  Is that what they call it? Easy to learn?

• 6:13Speaker 01

  Fun to master.

• 6:14Speaker 00

  Fun to master. But let's, let's try to master, master this faster. That was the challenge I gave to Adam Savage, one half of the Mythbusters. I said, can you make me one that makes it easier? And so he built me this. This is a machined Delrin Kendama. You'll notice it's a lot heavier.

• 6:37Speaker 01

  Okay. Here's the thing. You just throw that into conversation. Oh yeah. Adam Savage made me a version. For people who are watching slash listening to this, who haven't come across Adam Savage, he's like a massive, massive hero of mine, gigantic hero of mine. Okay. Let's give this a go. All right. It's much heavier. The ball is heavier and the handle is heavier.

• 6:56Speaker 00

  Before you use it, let me tell you what makes it special.

• 7:00Speaker 01

  Do you think it's easy with this one? Is it going to be easier?

• 7:02Speaker 00

  It should be easier for a couple of reasons.

• 7:04Speaker 01

  Okay.

• 7:04Speaker 00

  So first of all, it's made of Delrin, which is a, a plastic that you can machine on a lathe. And we made this to, uh, hopefully use physics to make it easier. So for example, the string is attached to the very center of the Dama of the ball. So when you lift it, you don't put a torque on the ball. So it comes straight up with that hole facing the ground and it doesn't get twisted as much.

• 7:34Speaker 01

  Cause in here, it might be at the, the sort of apex of the ball, but inside it's not sitting in the center.

• 7:41Speaker 00

  Exactly.

• 7:41Speaker 01

  It's just like a kind of random knot.

• 7:43Speaker 00

  Exactly. So you kind of have to like learn the personality of, of the Kendama. Whereas with this one, the physics should help us. Secondly, the Dama is really heavy and it's built to spin. So you can use gyroscopic stability to keep that hole facing down. Let me try this one.

• 8:05Speaker 01

  Okay, go on.

• 8:05Speaker 00

  Get it spinning.

• 8:08Speaker 00

  And then we'll lift it. Would have been really cool if that worked the first time.

• 8:14Speaker 01

  Let's pretend this is the first time.

• 8:16Speaker 00

  Okay.

• 8:20Speaker 00

  Beautiful, right?

• 8:21Speaker 01

  I'm so jealous.

• 8:23Speaker 00

  It's beautiful. Okay. Now you, you give it a try. I'll take out some of the spin on that string.

• 8:30Speaker 01

  Okay. Okay. So let me just think about this then. So because you've got the gyroscopic effect of it, because it's spinning around, it means that the ball is less likely to rotate in any axis other than the one that you can spike.

• 8:43Speaker 00

  Yeah. You just pull it straight up.

• 8:45Speaker 01

  Hang on, let me get it spinning.

• 8:47Speaker 00

  It doesn't need to spin too fast to, to be more stable. That actually was pretty close. I saw where the hole was.

• 8:57Speaker 00

  It's a bit unfair because you'll, what, what you'll notice if you look at the original Dama, it's got this.

• 9:02Speaker 01

  Gigantic.

• 9:02Speaker 00

  The hole's gigantic and it's, it's even easier to catch, whereas that hole is designed just to fit the spike dead on.

• 9:12Speaker 01

  Oh man. We have to get me doing it because otherwise it doesn't make sense.

• 9:15Speaker 00

  Pull, yeah. Pull it up a little less high.

• 9:18Speaker 01

  Okay.

• 9:20Speaker 00

  It helps also to imagine that you're stabbing the ball. You're not hoping that it lands on the spike. You're hoping to shove the spike into where the hole is.

• 9:29Speaker 01

  I'm sorry, guys. I've got to do it.

• 9:31Speaker 00

  No, no, no. This is fun.

• 9:35Speaker 00

  If you were standing, I think it would be a lot easier because the trick is to pull it straight up.

• 9:45Speaker 00

  That, I didn't think-

• 9:46Speaker 01

  How do you get it?

• 9:47Speaker 00

  That was amazing. That Dama went up like so high above the spike and yet it still fell right on the spike.

• 9:57Speaker 01

  I enjoyed that.

• 9:57Speaker 00

  Because again, it's so heavy and when it's spinning, it's just so much less likely for the hole that you need to go out of the way. It's like here, this is how I was and this is how I still am and it goes right on the spike. So I treasure this for the physics behind it and for the whole, the whole journey that we took.

• 10:17Speaker 01

  And how Adam Savage made it, amazing.

• 10:19Speaker 00

  That, that whole thing, exactly. You can watch an entire hour-long video on his Tested channel where I tell him, "I just would really like the Dama to be heavier." And he's like, "Okay, I've got a special machine that can build spheres on a lathe, whatever radius you want." And the same tool could be inverted to make the cups.

• 10:40Speaker 01

  Hmm.

• 10:41Speaker 00

  It can do a reverse sphere as well. And then the, the knurling on the handle is actually done with a lathe attachment for making the threads on a screw.

• 10:52Speaker 01

  So wait, what's, what material is it? It's like a plastic?

• 10:54Speaker 00

  Yeah, it's a plastic called Delrin.

• 10:56Speaker 01

  Okay.

• 10:57Speaker 00

  And it's a, it's a dense plastic that you can machine. Like if you put a softer plastic on a lathe, the blade would just grip it and the whole thing would break. It'd be very dangerous. But this, you can just zzzzz put a little blade on it while it spins and you just cut pieces away. You cut strings of it away. It's amazing.

• 11:16Speaker 01

  But then you end up with something that's more robust than if you 3D printed it, for example.

• 11:21Speaker 00

  More, more robust? Yeah, exactly. Exactly. It's very robust and it will, it's, it has some give. It won't wear away. Even, it'll even last longer than wood. I mean, no surprise, it's plastic. But-

• 11:33Speaker 01

  If I come back in 10,000 years, that'll still be there.

• 11:35Speaker 00

  It'll still be here. That's right.

• 11:37Speaker 01

  Still be relatively Dama.

• 11:38Speaker 00

  There will be, you know, whatever humans evolved into. What, 10,000 years, you said? Yeah, and it won't be that different. But they'll still be struggling with it. And-

• 11:48Speaker 01

  What about, what about these bits? Can you do like cool tricks with this stuff?

• 11:51Speaker 00

  Yeah, try to catch the ball in a cup.

• 11:53Speaker 01

  Okay.

• 11:54Speaker 00

  Like, trick with the cup is to just put the cup right underneath the ball. Oh, it turned. It turned. There's not enough friction.

• 12:04Speaker 01

  Do you know what this really reminds me of? The cup and ball thing?

• 12:06Speaker 00

  Hmm.

• 12:07Speaker 01

  So, um, when it comes to robots, uh, you'll have seen loads of really impressive videos of robots doing like backflips and then-

• 12:17Speaker 00

  Yeah.

• 12:18Speaker 01

  Running through forests and all of this amazing stuff. The thing about those robots is that they are, they're pre-programmed. They're sort of, is it like a script that they're following? So, uh, they can adjust it slightly for wind and, you know, terrain and things, but they're, but they're essentially like, someone has sat down and worked out exactly how they should move. If you get a robot to feel its way through a problem instead, they struggle way more.

• 12:43Speaker 00

  Ah, like a human?

• 12:44Speaker 01

  Like a human. And a few years ago, I got to go in, I mean, I've been several times, but in particular, a few years ago, I went to go into the robotic labs at DeepMind, where they were at the phase where they were teaching robots how to play cup and ball.

• 12:59Speaker 00

  Oh.

• 13:00Speaker 01

  That was what they were using as a way for the robot to understand its own limbs, to understand the environment, to understand physics, gravity, and so on, and so on, like the solidity of different things. And so- It's sort of, in a little, in a, in a way, it was a little bit sad that this robot was just there. I mean, it was just an arm, not a whole body. But this robot was just there like over and over again, like this, fail, okay? And then reset. And then over and over again, and then fail, and then reset. And it would be there overnight, day after day, after day, after day, after day, after day, just like, and go.

• 13:32Speaker 00

  You'd wanna help it.

• 13:34Speaker 01

  And fail.

• 13:34Speaker 00

  Even though giving people advice on this thing probably just annoys them. Let's see if I can catch it on, in the cup below.

• 13:43Speaker 01

  Oh, so close.

• 13:44Speaker 00

  So close. I feel like some parts of the Savage-designed Kendama are harder. For example, we already talked about how the hole is so much more narrow. I think the cups are also less deep.

• 13:59Speaker 01

  Yeah, they are. Um, this is great, though. This is, uh, this is, my kids don't need an iPad anymore. They've got one of these.

• 14:07Speaker 00

  Yeah, exactly. You know what toy my daughter recently fell in love with?

• 14:11Speaker 01

  Tell me.

• 14:12Speaker 00

  Paper yo-yos? Just the stick that's got a lot of paper, a long ribbon of paper wound up all around it. And so you can throw it like this-

• 14:21Speaker 01

  Right.

• 14:21Speaker 00

  Flick it and it shoots out. And she just played with that all day. And then at her birthday, she wanted to give one to every kid that came. And I'm like, I love that this paper on a stick is still so exciting to kids who have literally the entire world and history of media at their fingertips. They're still like, the properties of wrapped paper is so cool.

• 14:44Speaker 01

  Right, but that's, but that's who we are, you know? We, we love experimenting with our environment and like finding things that surprise and delight us.

• 14:52Speaker 00

  Exactly.

• 14:52Speaker 01

  It's all about, I mean, basically back to the robotics thing, you know, the way that our brains work is that we make predictions about what's gonna happen and then are delighted when the world meets our predictions. Exactly what the robots are doing. Um, yeah, and children and robots alike doing the same thing.

• 15:10Speaker 00

  And adults. So you can take that home and you can practice.

• 15:13Speaker 01

  Oh, I'm gonna, I'm gonna.

• 15:14Speaker 00

  And you'll be amazed. We, we actually made a custom Kendama with Kendama USA for the Curiosity Box years ago. I could not find one in the time that I was packing. But we put, um, holes in all the cups so that you could take these additional spikes and make it, make it a spike everywhere.

• 15:31Speaker 01

  Also doubles as a way to beat people up.

• 15:33Speaker 00

  Exactly. It became a weapon.

• 15:35Speaker 01

  If they were trying to bully you in the playground.

• 15:36Speaker 00

  Yeah. It became a weapon.

• 15:38Speaker 01

  Are they like Kendama world champions?

• 15:40Speaker 00

  Oh yeah. You should look up what some of the pros do. They are, you know, spinning the string around their finger and it's called juggling. I don't have anything else to say about it, except that I really treasure this as a memory of, of a build with Adam Savage, a deep dive into the physics of how it works. But also the lesson that even when you try to hack the physics and make the easiest Kendama to catch on a spike, you're still not that good at it. It still takes that human flesh neural network a lot of tries to get the knack of it.

• 16:19Speaker 01

  You certainly do.

• 16:19Speaker 00

  To get the physical memory of it.

• 16:21Speaker 01

  Hey, look, my main memory for this is that I, I managed to do it while standing up admittedly.

• 16:25Speaker 00

  You did.

• 16:25Speaker 01

  I did, I did manage.

• 16:26Speaker 00

  On your very first try, because of the way the editors put the clips together. Thank you, guys. This, here's a problem. This one, it's changed. I feel like the white plastic has expanded or the black has contracted. Because look, if I try to catch it on the cup, it rotates off. Like it's, doesn't have enough friction anymore. At the end of the day, things that are spinning are more stable because they, they accelerate differently in response to forces. Imagine you are, you're a piece of mass that's going around in a circle that's, uh, um, parallel to the plane of the floor. Okay? Let's say when you come around here to the front, I put a force on you right from above. Like

• 17:11Speaker 00

  I'm gonna push you down to the ground. What happens? Are you gonna go like this? Whoa, and just suddenly start spinning now perpendicular to the floor?

• 17:20Speaker 01

  Not.

• 17:20Speaker 00

  No. Your velocities combine. And now you go, you keep going counterclockwise around, parallel to the floor, but you're also gonna be going down a little bit. You're gonna go a combination. You're gonna go diagonally. But look at this diagonal motion. Now you go down and then you come back up and back down. So if you were, if you imagine that you were an entire disc, what's happened is someone has put a force in the front and you've moved that way. So the effects of the force are translated 90 degrees ahead in the rotation.

• 17:54Speaker 01

  Okay.

• 17:55Speaker 00

  So someone pushing right here feels an enormous amount of resistance. Because normally when we push things, they move in the direction of our force, but not a spinning object. It goes like that.

• 18:07Speaker 01

  Right.

• 18:07Speaker 00

  So any little torque, any, any rotating force applied to a spinning object is gonna cause it to behave differently. It's gonna cause a lot of resistance. So it stays stable where it is. Unless you put a lot of force on it. But if it's just, if it's just in a gimbal or something, then as the ship moves, the gyroscope goes, nah, nah, move around me. I've got way more inertia, or it feels like I have way more than you do. So that's why they're so stable.

• 18:35Speaker 01

  Which is why you have them on, on ships, for example.

• 18:39Speaker 00

  On ships to make a little gyro compass. And it just keeps pointing north. Because as the ship moves, the little like axles that hold this, uh, gyroscope in place, they're like, come with us. And it's like, you gotta try harder than that. And they're like, okay, we'll just go around you. And it just keeps pointing north.

• 18:58Speaker 01

  Right. But also, I guess on a ship, in particular, you've got these, so it's not just that you've got the one force pushing there at one point, because you're, you know, a moment in the future, you'll have another force in that direction. And if you are, if you are, uh, feeling that force, but averaging it with the existing velocity of it turning around in a circle, then you've just got a little bit more time, I guess, right?

• 19:21Speaker 00

  Yeah. And, and you have to make sure that the object is spinning fast enough that it barely gets moved by those forces. Um, so that it's spinning so fast and has so much, uh, or it's so heavy that a little touch here causes the smallest change 90 degrees ahead. Gravity tries to, to make it fall over this way and it goes like that and gravity goes, okay, fine, I'll, I'll tip you over that way and this way. And then it's processing.

• 19:48Speaker 01

  Mm-hmm.

• 19:48Speaker 00

  And that's why we see gyroscopes process like this, where they point their tops around in a circle until eventually they run out of energy.

• 19:56Speaker 01

  Should we go to a break?

• 19:57Speaker 00

  Yeah, let's go to a break.

• 19:58Speaker 01

  See if you can guess what I'm gonna be doing in the break.

• 20:01Speaker 00

  And, and we'll answer your questions when we come back.

• 20:04Speaker 01

  Certainly will.

• 20:19Speaker 00

  This episode is brought to you by Cancer Research UK.

• 20:22Speaker 01

  Dentist appointments, MOTs, routine checkups help us to spot faults early before we need a root canal or breakdown at the side of the road. And cancer screening is the same idea.

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  Research like this saves and improves lives.

• 21:08Speaker 00

  For more information about Cancer Research UK, their research and breakthroughs and how you can support them, visit cancerresearchuk.org/RestIsScience.

• 21:21Speaker 03

  This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome, that's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration blog, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense? There's no place like Chrome. Check responses, set up required compatibility and availability varies 18 plus.

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• 22:09Speaker 00

  Welcome back. It's time for your questions.

• 22:13Speaker 01

  Certainly is. First one, we've got one from Ben from email. Ben asks, are there any mathematical advantages that can be used when swimming? Is it possible to swim faster with the power of math? Okay, look, Ben, you're on my home turf here. We're in fluid dynamics, right?

• 22:29Speaker 00

  And math.

• 22:31Speaker 01

  I'm happy, happy. I'm happy, happy. Okay, here's the thing, right? When you are taught, did you do swimming lessons?

• 22:39Speaker 00

  Yeah, oh, yeah, oh, yeah.

• 22:40Speaker 01

  Okay, show me how you're taught to hold your hand in swimming lessons.

• 22:45Speaker 00

  Like a little cup?

• 22:46Speaker 01

  Math says no. Math says no.

• 22:48Speaker 00

  What should I be doing?

• 22:49Speaker 01

  Okay, so here's the thing, right? If you, if you had like paddles for hands, right, you would, you would do way, way better at swimming. This is one of the reasons why you look at sort of professional athletes, professional swimmers, and they do, they should have got these shovels, like giant shovel hands.

• 23:05Speaker 00

  Oh, right. There's still gaps between the fingers, but they keep them spread?

• 23:08Speaker 01

  They keep them spread because you can make it bigger. And the reason why you can make it bigger is because, I mean, if you go too far, then yeah, the, the water-

• 23:15Speaker 00

  It's like a comb, but closer.

• 23:17Speaker 01

  But closer, you can get little eddies that appear between your fingers, so you can increase the size of your hand.

• 23:23Speaker 00

  Without more flesh?

• 23:25Speaker 01

  Without more flesh.

• 23:26Speaker 00

  Oh, wow.

• 23:27Speaker 01

  Right? So what you should do is basically like a natural hand position.

• 23:30Speaker 00

  Uh huh.

• 23:30Speaker 01

  And there are real legitimate scientists that have looked into this, by the way, that have like, have done all of the, all of the calculations about what your hand should be. So it's like, essentially your, your natural resting hand position, that is how you should be shoveling water.

• 23:45Speaker 00

  That, I bet this isn't true, but I've always wondered why our resting hand position is the way it is. Why, when I flex no muscles, is my hand not like this or like this?

• 23:56Speaker 01

  Yeah.

• 23:57Speaker 00

  Why is it kind of this weird?

• 23:59Speaker 01

  Intermediate.

• 23:59Speaker 00

  Intermediate thing. And I haven't heard a definitive answer. There's just a lot of speculation that like, well, that gives you the best leverage on both sides, the muscles only have half as much to do from rest versus like, if my hand was always at rest like this, then closing it would require a lot of really long muscle that was, had a lot of work to do against the natural phase and vice versa.

• 24:29Speaker 01

  So it's like you're in your average position, essentially?

• 24:31Speaker 00

  But the fact that our, our resting position is ideal for swimming and pushing fluids makes me revisit the aquatic ape theory, huh? We evolved to be water people.

• 24:44Speaker 01

  I love the aquatic ape theory.

• 24:46Speaker 00

  Yeah.

• 24:46Speaker 01

  It's one of my favorite examples of how you can tie together evidence, basically makes it look like you can prove any argument by induction, essentially. You could say, look, we've got blubber like attached to our skin. Do you know who else has got that? Whales and dolphins. We breathe air. You know who else does that?

• 25:05Speaker 00

  Whales.

• 25:05Speaker 01

  Whales and dolphins. We don't have any hair on our bodies. You know who else doesn't? Whales and dolphins, and so on and so on.

• 25:12Speaker 00

  Exactly. And then as long as you give it a really clever name, aquatic ape, stoned ape, like people go, oh, wow. Now, now it's got like a banner, it's got a team name? I, I'd get behind that.

• 25:26Speaker 01

  Yeah, unfortunately, don't get behind it because there's way more evidence that we weren't aquatic, aquatic apes than that we were. Okay, other things you can do with swimming. Basically, a lot of it is about streamlining your body. So you want to be long and thin. The more streamlined you can be, the better. So there were swimsuits a few years ago that would compress your body as much as possible. You have to like literally squeeze yourself into them because the smaller the surface area, the, the, the less drag that you'll be creating. There was also swimsuits where they had, okay, so it's sort of a flotation, effectively, in the back that would keep your legs up higher and again, to reduce drag, and that would have certain little inlets on the surface of the, of the costume

• 26:11Speaker 01

  that would allow the water to slip off it much easier. At that point, all of the records of swimming just went down, down, down, down, down.

• 26:17Speaker 00

  Yeah.

• 26:18Speaker 01

  And then I think they banned them.

• 26:19Speaker 00

  Yep.

• 26:20Speaker 01

  I think they banned them and now we're sort of back to like, no, what's your, what's your flabby little flesh body gonna do with this?

• 26:26Speaker 00

  Can it do on its own? Yeah, yeah.

• 26:28Speaker 01

  But that's the main one. The main one is, yeah.

• 26:31Speaker 00

  The hand position.

• 26:31Speaker 01

  Swim in a straight line. That's a shortest distance.

• 26:34Speaker 00

  Mathematically, yeah, yeah, that's a good one.

• 26:36Speaker 01

  And swim with your hand like an aquatic ape. Okay, question for you. This is from Neil Fresh, who sent in an email, despite his name sounding very Reddit-like. Since Jupiter is a gas giant, what would happen if you flew right through the middle of it?

• 26:50Speaker 00

  You would, you would not make it through. We've actually learned a lot about the inside of Jupiter recently. Before Juno went around Jupiter, it launched in 2011. I don't know when we got the results back, but before 2011 for sure, people did not know what was in the middle of Jupiter. We still don't really. But there were kind of two competing theories. One was that there's nothing. It really is a gas giant. It's just gas all the way down. The other theory was that, no, it might have a big, hard, rocky core. Like, if Earth was 20 times more massive, it would have enough gravity to hold on to hydrogen. Maybe that's what Jupiter did. Maybe it has a surface. It's a rocky planet

• 27:35Speaker 00

  that's surrounded by, you know, hundreds and hundreds of miles of gas. So the Juno satellite orbited around Jupiter, measuring its gravitational anomalies across the surface to kind of figure out what's underneath and what its sort of composition is and how symmetric it is. As it turns out, it is not only, it's not just gaseous all the way through. It doesn't have a core though, either. The answer's somewhere in between. It's got what they call a fuzzy core. And it maybe isn't, isn't solid in the middle, but it's incredibly dense. We don't even really know what hydrogen in this sort of supercritical phase is going

• 28:17Speaker 00

  to behave like. We call it a liquid metal, but it's not like mercury. It's probably not metal colored, but it's very electrically conductive. That's what makes it a metal. And so that might explain Jupiter's extremely strong magnetic field, that it's this very fast spinning, electrically conductive ball. So if you tried to just fall into Jupiter or and shoot out the other end, you would hit this dense ocean, this slowly more and more dense gradient of hydrogen that became more and more dense. It doesn't have a, a surface with an atmosphere above it. It just becomes more and more thick and dense as you get to the middle.

• 28:58Speaker 01

  Would you, but hold on there. You said you wouldn't be able to pass through it. So, okay, I accept that it's like dense and thick, but has it ever become solid or is it still liquidy?

• 29:06Speaker 00

  It's still liquidy. I, we're, we're not entirely sure though. There, you know, there could be the heaviest metals in the middle, but what state they will be in under the kind of pressure they would be in, it's not like, oh, yeah, eventually you drop a coin, whoops, down onto Jupiter, it's gonna land on this hard surface in the middle. It's gonna get lost in the fuzzy, gurgling mess that is the gradient of its density. So if you tried to go through it, there's no known material that would not get crushed up and, and phase changed in the middle.

• 29:47Speaker 01

  Right. Well, there you go. That's my ambition off, off the cards.

• 29:51Speaker 00

  It'd be a way to go.

• 29:52Speaker 01

  I was about to make a reference about swearing inside it, but that was a different thing.

• 29:57Speaker 00

  That was a different thing.

• 29:58Speaker 01

  It's a different thing.

• 29:59Speaker 00

  The first, the first to say a bad word in Jupiter's gooey middle.

• 30:04Speaker 01

  Wait, the Juno probe, where did it actually go?

• 30:09Speaker 00

  Well, I know Jupiter for sure, but it didn't go to other places.

• 30:12Speaker 01

  Did it go in any, just passed?

• 30:14Speaker 00

  It had this big elliptical orbit and it would come really close to Jupiter and then fly way back out. And it did that like scan thing where it scanned like slices over time so that we could learn from how its uh, speed changed very slightly, like even by a tenth of a millimeter per second, we could tell based on the radio waves it sent back, how it was being changed by what happened to be underneath it on Jupiter. So we could get this really detailed look at what the density of the mass is where.

• 30:46Speaker 01

  That's amazing.

• 30:47Speaker 00

  Yeah.

• 30:47Speaker 01

  And then presumably it flew off into space. It didn't come back.

• 30:50Speaker 00

  No, it didn't come back, but I don't know if it, it's not the one that went off to other planets later, was it?

• 30:57Speaker 01

  It does just feel like a bit of a missed opportunity to not nosedive into it at the end.

• 31:01Speaker 00

  I guess we've, we've crashed them into Saturn. We, we don't want to bother any potential life forms that might live in places. So I know that we won't crash probes onto the jovial or Saturnine moons.

• 31:15Speaker 01

  Just in case.

• 31:16Speaker 00

  Just in case. But I don't know, Juno may have crashed into Jupiter. I don't actually know its final fate.

• 31:21Speaker 01

  Let me look it up.

• 31:22Speaker 00

  Did it get slingshot off eventually? Is it still orbiting?

• 31:27Speaker 01

  Where is it now? It's still alive. It's still orbiting Jupiter. It's still there.

• 31:30Speaker 00

  Oh, good for Juno.

• 31:32Speaker 01

  Good for Juno. It's, it's approved to continue operating until its hardware finally gives out and contact is lost. Eventually it will go into Jupiter.

• 31:41Speaker 00

  Okay. All right.

• 31:42Speaker 01

  But it'll be a slow, natural death rather than a controlled dive.

• 31:44Speaker 00

  I wonder how long it could give us reports of what it was detecting as it fell into Jupiter?

• 31:51Speaker 01

  Hmm.

• 31:51Speaker 00

  I'm sure there's not like a big 4K camera on it. So we could really see the insides. I wonder how quickly it gets dark.

• 31:58Speaker 01

  Inside Jupiter.

• 31:58Speaker 00

  Inside Jupiter, on the, on the sun facing side as you fall in, when does it become dark as night? But you're still falling.

• 32:07Speaker 01

  Because the clouds, clouds, I mean, it'd be discolored pretty quickly, wouldn't it?

• 32:12Speaker 00

  Yeah. But I mean, how quickly? Cause it's, it's like mainly hydrogen gas and other gases, but you could probably fall for 200 miles and still like see out into space.

• 32:26Speaker 01

  Really scary about that.

• 32:27Speaker 00

  I'm still not even close to breaking the kind of outside.

• 32:32Speaker 01

  Amazing. Okay. Last question. This is a question from Matt, who asked this question on Spotify. Uh, Matt says, which books would you recommend for an adult interested in getting back into maths, stats and statistics some years after high school?

• 32:46Speaker 00

  I would love to hear your answer to this.

• 32:47Speaker 01

  Okay. Right. Here's the thing. I think textbooks are literally designed for this, you know? Like that's the whole point is to start you at the beginning and walk your hand through and pick up incrementally on the ideas one after the other, the other. There are a few textbooks, um, that I think are terrible. There's quite a lot of them I think are terrible. The famous, okay, the famous American one, the calculus one, hang on, the Stewart book for calculus. Right. This literally brings me out in hives. Maybe it's just the way my brain works, but it just, oh God, it's been so long defining limits before you actually get to any of the juicy, delicious stuff.

• 33:28Speaker 00

  Okay.

• 33:28Speaker 01

  In a really, really laborious way. It's like, you know what? If I learn how to play the piano as an adult, I don't want to spend four years on scales before I get to just try something.

• 33:41Speaker 00

  Right.

• 33:41Speaker 01

  Maybe I'm not going to be very good at it. Maybe I'll only be able to do like a little section of it, but I want to like play with it. I want to like enjoy the process. I don't just want to like hammer myself over it.

• 33:51Speaker 00

  Okay. So Stewart calculus, not good. Now, I really like the Spivick.

• 33:56Speaker 01

  Spivick one. Okay. Did you, you mentioned this on here before.

• 34:00Speaker 00

  I may have mentioned it before.

• 34:01Speaker 01

  Oh yes, this one is nice. Yes. Because it has lots of examples, right? It's sort of like projectiles.

• 34:07Speaker 00

  It does a lot of, okay, let's define a limit. And it goes, well, it's obviously just this. Okay. Well, if that's what it is, here's a problem. And you keep going, oh my God, it's almost like a drama. You're like, oh, you're right. It can't be that. And eventually it gets down to like, look, like what a function is, it just blew my mind. And at the end, it's like, look, all you can say is a function is a bunch of ordered pairs. Um, specifically where what? Like there's a, the second number only is ever assigned to one first number. And you're like, that's it. That's a function.

• 34:41Speaker 01

  That's a function.

• 34:42Speaker 00

  And I get why, and I get why it can't be anything else. It really was just like a page turner.

• 34:48Speaker 01

  See, that's it. That's what, that's what you want in a really good textbook is that you're, you're starting with stuff that feels, that is extremely fundamental, extremely basic in a lot of ways, but it feels really revelatory, you know? I think this is actually, if I'm honest with you, this is what I think you do really well. You take things that feel really obvious on the surface and then make them feel like a great discovery, this giant discovery. I think really good textbooks do that. The other types of textbooks that I really like are the ones where it's really anchored in tangible ideas. So the one for statistics that I really like, and I go back to it all the time, because I just think the explanations are so good. And it's called Beginning Statistics, An Introduction for Social Scientists.

• 35:32Speaker 00

  Who's it by?

• 35:33Speaker 01

  It's by Ian Diamond and Julie Jeffries. It's not big. It's not chunky. It's just really plain language. And because it's for social scientists, all of the examples are anchored in people and what people are doing and how people change, which is how statistics was created in the first place, right? Like statistics was the science of studying individuals and how they vary between one another.

• 35:57Speaker 00

  Yeah. I, I find that really helpful with statistics especially. I, I cannot learn the difference between a geometric and a harmonic mean. If you just show me an equation and then you say, oh, it's this ratio. Like I need you to say, look, if you're talking about how population grows.

• 36:14Speaker 01

  Right.

• 36:15Speaker 00

  Geometric mean is better than, than the arithmetic mean. And here's why. And I go, I get it. Okay.

• 36:21Speaker 01

  Or if you're like, okay, um, we've got this exam that's been marked over here and this exam has been marked over here. How can we possibly compare the two? What can you possibly do to say this student is better than this student, even though they studied different exams? It's like, well, yeah, of course you need a Z score. You get it, right?

• 36:37Speaker 00

  Yeah.

• 36:38Speaker 01

  So, so those are the ones that I really like. The other one that I really like, um, is there's a Stroud textbook, which is called Engineering Mathematics. And I like that one as well, because it's just, it's very practical. It's very sort of like, okay, you want to build a bridge, you know? What the hell do you need to do to build a bridge?

• 36:55Speaker 00

  Okay.

• 36:56Speaker 01

  So these aren't like pure mathematical ones. You know, if you like the pure stuff, there's, there's other places to go, but these are the ones that, that I particularly like. Um, yeah, but you, I mean, it's textbooks. That's literally what they're for. That's literally what they're for. Just really miss those days where you would get a massive textbook and your whole job was to go through it. Oh, the luxury, the luxury that somebody else has thought about your path from where you are.

• 37:20Speaker 00

  Yep.

• 37:20Speaker 01

  To where you need to get to and like incrementally advanced each piece of knowledge for you.

• 37:26Speaker 00

  It can feel embarrassing to be like, I'm going to read a textbook, but they actually are, yeah, they are one of the best ways to learn and to go on a journey as opposed to just like, oh, here's some kind of cool facts.

• 37:43Speaker 01

  Right.

• 37:43Speaker 00

  That the reviewers can write up in their review about like, oh, did you know this about Saturn?

• 37:49Speaker 01

  Did you know this about the center of Jupiter?

• 37:51Speaker 00

  What's, what's your favorite book that you've written?

• 37:55Speaker 01

  My favorite book that I've written? I, I, do you know what? I dislike everything I've ever written.

• 37:59Speaker 00

  Okay. I thought you might say that, but if you, if someone was like, where should I start?

• 38:05Speaker 01

  With stuff that I've written.

• 38:06Speaker 00

  I'm going to judge you based on this one book of yours that I read. Which one would you recommend?

• 38:10Speaker 01

  Then it's Hello World.

• 38:12Speaker 00

  Hello World. Okay.

• 38:13Speaker 01

  Which I wrote in 2017, 2018. It's about, it's called How to Be Human in the Age of the Machine. And it's about, um, essentially how, how people everywhere are increasingly applying mathematical algorithms to making decisions. I mean, sort of turns out I was right.

• 38:34Speaker 01

  And, uh, and it's all about the really big problems that can arise unless you think about how to do that really carefully. And what, the reason why I'm putting this one forward is that it was written a long time ago, right? This is like 6,000 years ago in the.

• 38:50Speaker 00

  Yeah.

• 38:51Speaker 01

  In technological terms, yeah. Really, really long time ago. And honestly, every now and then I go back to it and it's like, yeah.

• 38:58Speaker 00

  Yeah.

• 38:58Speaker 01

  Yeah. Still, yeah, still applies.

• 39:01Speaker 00

  Hello world.

• 39:02Speaker 01

  Hello world.

• 39:02Speaker 00

  Goodbye viewers.

• 39:05Speaker 00

  Thanks for watching.

• 39:06Speaker 01

  Gosh, you're slick.

• 39:08Speaker 00

  Send in your questions to [email protected].

• 39:12Speaker 01

  Or join us on our Reddit, our subreddit, therestis-science, I think.

• 39:17Speaker 00

  Or leave comments down below. Uh, that, that gives us engagement, right? In fact, do both. Comment it, but then also email it and say you commented and liked and subscribed and hit that bell.

• 39:30Speaker 01

  Yeah.

• 39:30Speaker 00

  And then we'll be more likely to answer it. No, just kidding. I would never do that. You're all equal in my eyes. We love you no matter what you do.

• 39:37Speaker 01

  We'll see you next time.

• 39:56Speaker 05

  Hi everybody. It's Dominic Sambrook here from The Rest is History and we are here to tell you about a thrilling new series on the blood soaked climax of the French Revolution, The Reign of Terror.

• 40:10Speaker 06

  So the French Revolution is one of the most significant episodes in the whole of world history. It essentially lays the foundations for contemporary politics as we know it, but it is also unbelievably dramatic. We'll be discussing the murder of the firebrand Jean Paul Marat in his bathtub. We will be going to the guillotine with Marie Antoinette.

• 40:33Speaker 05

  And in our final episode, we will be telling the story of the extraordinary grotesque downfall of one of the chief architects of the terror, one of the most evil men in history, some would say, Maximilien Croesus-Bier.

• 40:49Speaker 06

  So if you want to hear this epic series, search for The Rest is History wherever you get your podcasts.

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  Everyone's got a hard question about AI, your job, your kids, where it's going. Anthropic was built to surface those questions and share what it finds along the way, because there's hope in hard questions. Ask yours at claud.ai/spotify and keep thinking. That's claud.ai/spotify.

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